1. The Field of the Invention
The present invention relates generally to electromagnetic interference (EMI) shields for transmitter, receiver, transponder, or transceiver modules.
2. The Related Technology
Pluggable transceiver modules are of interest in a variety of communication systems. A z-axis pluggable transceiver module is designed to be slid into a receptacle. Appropriate power supply and signal connections are engaged when the module is locked into its fully inserted position.
One problem associated with pluggable transceiver modules is achieving a high attenuation factor for electromagnetic interference (EMI) generated by the electronics in the module. This is of particular concern for high data rate transceivers. As is known in the art of high frequency electronics, an increase in the data rate of high-speed electronics tends to increase the emission of high-frequency EMI radiation. Moreover, high frequency EMI emissions can penetrate even comparatively small gaps in EMI shielding. Consequently, greater care must be taken in high data rate transceivers to achieve adequate EMI shielding.
Some of the problems associated with shielding high data rate transceiver modules can be illustrated with reference to FIG. 1. FIG. 1 is an exploded perspective drawing of z-axis hot pluggable module that has been proposed by the 10-Gigabit Small Form-factor Pluggable (XFP) Module Group, a module Multi Source Agreement (XFP-MSA) association. The XFP-MSA is an association of companies developing a specification for a 10 Gb/s transceiver module having compatible mechanical and electrical features.
Referring again to FIG. 1, a transceiver module 10 is designed to slide into a cage assembly 12. A host board 14 includes a so-called “right angle” surface-mount connector 16 that fits through a bottom rear end opening of the cage. The rear end of the transceiver module includes a printed circuit board having an edge connector. The edge connector is inserted into a receptacle of right angle surface mount connector 16. The host signal interface includes the right angle surface mount connector 16 and associated high-speed interconnects. For XFP modules there is an associated 10 Gb/s serial interface (XFI), which is the high speed serial electrical interface for connecting a high data rate signal source (e.g., to a serializer/deserializer) to the transceiver module, with the XFI channel including the right angle connector 16, host board 14, traces, and any associated vias (not shown). A heat sink 20 is mounted to the cage 12 with a clip 22 to facilitate removing heat from the module.
A problem associated with the z-axis pluggable module is that sufficient clearance must be maintained to allow insertion and extraction of the module. This makes it difficult to achieve a high degree of EMI shielding, particularly in the rear of the module about the connector. Referring to the side view of FIG. 2, one approach that has been proposed is to include an EMI gasket 24 mounted on the rear of the cage 12, so that there is additional EMI shielding disposed behind the right angle electrical connector 16 during normal use. However, this arrangement does not provide a complete EMI seal around the rear of the module 10, especially in the region of cage opening 26 through which the right angle connector 16 extends. Consequently, EMI may leak out from the rear of the cage about the connector 16.
Therefore what is desired is improved shielding of EMI emitted from the rear-end of pluggable transceiver modules.